The new field of epigenetics is showing how your environment and your choices can influence your genetic code  and that of your kids

Three generations: Dr. Lars Olov Bygren, with son Magnus and grandson Ludvig in Stockholm

The remote, snow-swept expanses of northern Sweden are an unlikely place to begin a story about cutting-edge genetic science. The kingdom's northernmost county, Norrbotten, is nearly free of human life; an average of just six people live in each square mile. And yet this tiny population can reveal a lot about how genes work in our everyday lives.

Norrbotten is so isolated that in the 19th century, if the harvest was bad, people starved. The starving years were all the crueler for their unpredictability. For instance, 1800, 1812, 1821, 1836 and 1856 were years of total crop failure...